Motorized pipette

Abstract

A pipette is described comprising a piston for generating pressure to eject liquid and a motor for moving the piston. A drive-decoupling mechanism is interposed between the motor and piston to allow the motor to decouple and overtravel without causing the piston to overtravel.

What is claimed is: 
     
       1. In a pipette comprising a pressure chamber, a piston for generating pressure within the chamber, and means for moving said piston between a withdrawn position and an extended position providing predetermined maximum liquid ejection, said means including (i) a motor susceptible to overtravel when activating power to the motor is terminated, (ii) drive means coupling said motor to said piston to move said piston between said withdrawn position and said extending position, (iii) means for alternately connecting and disconnecting said motor to and from a source of such activating power, and (iv) means for reversing said motor; the improvement wherein said pipette further includes drive-decoupling means for decoupling the drive of said piston from that of said drive means when said piston arrives at either one of said two positions from the other position,   whereby overtravel of said motor does not cause said piston to overtravel,   said drive-decoupling means comprising   (a) a shuttle secured to said piston and mounted for linear movement within said pipette from a first position corresponding to one of said positions of said piston, to a final position corresponding to the other of said piston positions,   (b) a resilient member integral with said shuttle and secured to said drive means to transmit driving force from said drive means to said shuttle when the latter is between said first and said final positions,   said resilient member further comprising a bistable mechanical flip-flop that is integral with said shuttle and is secured to said drive means, said flip-flop occupying either a position distal to or proximal to said piston, depending upon whether said shuttle has last reached said final position or said first position, respectively,   and stop means for limiting the travel of said shuttle to only points between said first and said final positions,   said flip-flop having a resiliency sufficient, when said shuttle strikes said stop means, to allow said motor to overtravel while said shuttle remains motionless.   
     
     
       2. A pipette as defined in claim 1, wherein said mechanical flip-flop recouples the drive connection between said piston and said drive means when said motor is reversed. 
     
     
       3. A pipette as defined in claim 1, and further including reset means for resetting the position of said piston relative to said drive means for the next overtravel occurrence, simultaneous with said drive-decoupling means decoupling said piston from said drive means.